AAAS: Martinis & Freedman discuss Quantum computing at AAAS kick-off

"John Martinis and his colleagues at the University of California, Santa
Barbara (UCSB), have been trying to forge qubits from
superconducting circuits. In a superconductor, electrons do not travel
solo. Instead, for complicated quantum-mechanical reasons, they pair up
(for the same reasons, the pairs feel no electrical resistance). When
they do so, the pairs start behaving like a single particle, superposing
proclivities and all. This superparticle can, for instance, in effect
be moving in two directions at once. As electrons move, they create a
magnetic field. Make a closed loop of superconducting wire, then, and
you get a magnetic field which can be facing up and down at the same
time. You have yourself a superconducting qubit—or five, the number Dr
Martinis has so far managed to entangle.

Michael Freedman is trying to address this problem by taking a
different tack. Together with his colleagues at Microsoft’s Station Q
research centre, also at UCSB, he is trying to build what he calls a
topological quantum computer. This uses a superconductor on top of a
layer of an exotic material called indium antimony. When a voltage is
applied to this sandwich, the whole lot becomes a quantum system capable
of existing in superposed states.

Where Dr Freedman’s qubits differ from Dr Martinis’s is in the way
they react to interference. Nudge any electron in a superconducting
circuit and the whole lot decoheres. Dr Freedman’s design, however, is
invulnerable to such local disruptions thanks to the peculiar way in
which energy is distributed throughout indium antimony. The Microsoft
team has yet to create a functioning qubit, but hopes to do so soon, and
is searching for other materials in which to repeat the same trick." READ MORE (The Economist)